The proliferation of various wireless communication devices and systems has resulted in the need for improved solutions for antennas. This need is particularly acute in installations such as vehicles where space is at a premium, and where for certain applications such as military, police and some commercial installations, it is highly desirable to provide continuous coverage across a wide range of frequencies. While vehicles can employ multiple separate antennas that are individually designed to communicate effectively within a particular frequency band, it is far more convenient a single antenna can provide coverage over a wide range of frequencies.
It is also important to be able to communicate without knowing the relative orientation of the transmit and receive antennas in advance. For example, in the case of communication from a satellite to a terrestrial vehicle, as the vehicle moves about the terrain (or even within a building), signals will arrive at the antenna with a variety of different polarizations from different directions. If the vehicle uses, for example, a simple vertical dipole, one obtains 360° coverage but only for vertically polarized signals. Such a vertical dipole is relatively insensitive to horizontally polarized signals.
Many antennas mounted on vehicles also take the form of a mast that may be purposely flexible so that if the antenna hits an object it will bend and not snap or break. Antennas formed with flexible masts thus have their vertical and/or horizontal orientation direction altered by the flexibility of the mast, meaning that reliable communication cannot always be established if the polarization direction of the antenna is not exactly aligned with that of the transmitter. In short, it is often the case that as the vehicle moves throughout an environment its antenna may tilt at various angles and therefore compromise communications with either a terrestrial base station or a satellite.
One whip style antenna capable of operating in multiple bands was described in United States patent application publication number US 2010/0283699 published on Nov. 11, 2010 entitled “Broadband Whip Antenna”. This antenna includes multiple in-line dipole elements, selected ones of which have shielded meander line chokes enable switching from an extended dipole at the lower frequencies to a shortened dipole at the higher frequencies.